Switching assembly for a hydraulic pump jack

ABSTRACT

A switching assembly for a hydraulic pump jack has a non-magnetic cylinder. A piston is reciprocally movable within the interior bore of the cylinder. The piston has circumferential sealing means to engage the interior surface of the cylinder. A magnetic element is carried by the piston. A fluid source supplies a working fluid to the cylinder, wherein the piston is moved by injecting working fluid into the cylinder. At least one magnetic sensor is externally mounted adjacent to the non-magnetic cylinder that senses at least a top of a piston stroke and the bottom of the piston stroke. A controller receives signals from the magnetically actuated sensor as the magnet element carried by the piston comes in proximity with and influences the at least one magnetic sensor. The controller controls piston positioning by selectively controlling the working fluid supplied by the fluid source to the cylinder.

FIELD

The present switching assembly is intended for use with a hydraulic pumpjack to improve switching by more accurately determining piston positionand speed.

BACKGROUND

Switching assemblies presently used for hydraulic pump jacks consist oftwo axially spaced ports equipped with fittings in which are positionedelectric over hydraulic switches. The positioning of these portsdetermines the upper limit and the lower limit of the piston stroke. Theelectric over hydraulic switches are tied into an electricallycontrolled hydraulic spool valve. Variations in hydraulic pressure atthe ports results in the switches causing the hydraulic spool valve toreverse the direction and flow of hydraulic working fluid.

SUMMARY

There is provided a switching assembly for a hydraulic pump jack,comprising a non-magnetic cylinder with an exterior surface and aninterior surface that defines an interior bore. A piston is reciprocallymovable within the interior bore of the cylinder, the piston havingcircumferential sealing means to engage the interior surface of thecylinder. A magnetic element is carried by the piston. A fluid sourcesupplies a working fluid to the cylinder, wherein the piston is moved byinjecting working fluid into the cylinder. At least one magnetic sensoris externally mounted adjacent to the non-magnetic cylinder that sensesat least a top of a piston stroke and the bottom of the piston stroke. Acontroller receives signals from the magnetically actuated sensor as themagnet element carried by the piston comes in proximity with andinfluences the at least one magnetic sensor. The controller controlspiston positioning by selectively controlling the working fluid suppliedby the fluid source to the cylinder.

According to another aspect, the cylinder may have a lower end and anupper end with the upper end being higher than the lower end. Theworking fluid serves to raise the piston from the lower end toward theupper end, and gravity serves to return the piston from the upper end tothe lower end.

According to another aspect, the magnetic sensor may be a lineardisplacement transducer sensor bar that extends along the height of thenon-magnetic cylinder.

According to another aspect, the switching assembly may further comprisea seal for sealing the well when the piston is in a lower position, thenon-magnetic cylinder being removable to expose the piston in the lowerposition.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features will become more apparent from the followingdescription in which reference is made to the appended drawings, thedrawings are for the purpose of illustration only and are not intendedto be in any way limiting, wherein:

FIG. 1 is a perspective view of a switching assembly for a hydraulicpump jack.

FIG. 2 is a side elevation view of the hydraulic pump jack from theswitching assembly of FIG. 1.

FIG. 3 is a side elevation view, in section, of the hydraulic pump jackfrom the switching assembly of FIG. 1.

FIG. 4 is a side elevation view of a piston.

FIG. 5 is a detailed side elevation view, in section, of the piston in alower, locked position.

DETAILED DESCRIPTION

A switching assembly for a hydraulic pump jack generally identified byreference numeral 10, will now be described with reference to FIG. 1through 5.

Structure and Relationship of Parts:

Referring to FIG. 1, a switching assembly for a hydraulic pump jack 10includes a non-magnetic cylinder 12 in combination with a control unit18 that includes an electronic controller and a hydraulic fluid source(concealed within control unit 18). Referring to FIG. 3, positionedwithin non-magnetic cylinder 12 is a piston 14. Referring to FIG. 4, amagnetic element 16 is mounted on piston 14. Referring to FIG. 3, anexternally mounted magnetically triggered sensor 20 extends along thelength of non-magnetic cylinder 12 that is responsive to the position ofpiston 14. In one example, sensor 20 is a linear displacement transducer(“LDT”) that employs magnetostrictive technology. A magnetostrictive LDTworks roughly as follows. An interrogation pulse is transmitted along awaveguide in the sensor bar. When the magnetic field generated by thepulse interacts with the magnetic field of a permanent magnet that ispositioned somewhere along the waveguide, a strain pulse is generatedand returned back toward the transmitter. The time elapsed between thetransmitting the interrogation pulse the receiving the strain pulse isproportional to the distance between the transmitter and the permanentmagnet. A processor then converts the elapsed time into an electricalsignal that represents the distance between the transmitter and thepermanent magnet. In the present example, the LDT sensor bar 20 ismounted on the outside of the lifting cylinder 12 and the permanentmagnet 16 is located inside of the cylinder 12, and travels up and downwith the polish rod, such as on piston 14 as shown. As the permanentmagnet 16 travels up and down, sensor bar 20 measures the distancebetween the transmitter and the magnet, which relates to the position ofpiston 14, with an accuracy that may approach +/−0.1″. The electricaloutput signal representing the position of the polish rod may be updatedat much as 300 times per second or more. It will be recognized by thoseof ordinary skill in the art that other magnetically actuated switchesmay also be used that determine the position, and sensor 20 may includemultiple sensing elements, or multiple types of sensors. If discretesensors are used, at least two are required: one for the top, andanother for the bottom.

Referring to FIG. 1, control unit 18 receives signals from themagnetically triggered sensor 20 and is able to determine the positionof piston 14.

Referring to FIG. 2, the non-magnetic cylinder 12 has an exteriorsurface 24, a lower end 30 and an upper end 32 that is higher than thelower end 30. Referring to FIG. 3, the non-magnetic cylinder includes aninterior surface 26 that defines an interior bore 28. Piston 14 isreciprocally movable within the interior bore 28 of the cylinder 12

Referring to FIG. 5, piston 14 has circumferential seals 34 to engagethe interior surface 26 of the cylinder 12. Referring to FIG. 1, thehydraulic fluid source within control unit 18 supplies a hydraulicworking fluid to the cylinder 12. Referring to FIG. 3, the hydraulicworking fluid causes the piston 14 to be raised from the lower end 30toward the upper end 32 by an injection of working fluid 36 into thecylinder 12. The piston 14 returns from the upper end 32 to the lowerend 30 by force of gravity.

Referring to FIG. 3, sensor 20 is mounted to the exterior surface 24 ofthe cylinder 12 in axially spaced regular intervals. As shown, sensorbar 20 spans the full length of the non-magnetic stainless steelcylinder 12, and an electronic instrument is wired to this sensor barand reads the signal generated by the magnet in a particular location.

Referring to FIG. 3, magnetically triggered sensor 20 is excited as themagnetic element 16 carried by the piston 14 comes in proximity witheither the discrete sensors, or, in the preferred embodiment, as itinfluences the magnetic field within the LDT bar. This enables theelectronic controller within control unit 18 to determine precise pistonpositioning based upon the unique sensor value of the signals receivedand control movement of piston 14 by selectively controlling the workingfluid supplied to the cylinder 12. In one embodiment, the LDT bar 20allows the electronic controller to know where the piston is in itstravel within 0.1″ inches of movement such that it can adjust the supplyof hydraulic fluid to speed up or slow down to the programmed strokesper minute. When sensor 20 is an LDT bar, the stroke length can beprogrammed to start and stop at any desired location along the length ofcylinder 12.

Operation:

In the description below, the embodiment that uses the LDT bar isdescribed. Referring to FIG. 3, hydraulic working fluid supplied by thehydraulic fluid source within control unit 18, enters the cylinder 12causing the piston 14 to rise towards the upper end 32 of the cylinder12, away from the lower end 30. As the piston 14 moves upwards, themagnetic element 16 (best shown in FIG. 4) interacts with sensor bar 20.Signals from the LDT sensor bar 20 are sent to an electronic controllerwithin control unit 18. The electronic controller determines precisepiston positioning and controls movement by selectively controlled theworking fluid supplied to the cylinder 12. At the termination of eachstroke, the force of gravity is used to move the piston 14 downwardstowards lower end 30 and away from upper end 32.

Advantages:

To increase or decrease the speed of the cylinder with prior art devicesis a complicated process of adjusting the flow of the pump and timingthe strokes by watching a pressure gauge. When the pressure goes high,the time clock is activated and when the pressure goes low it isstopped. The time elapsed is then used to calculate the speed of thecylinder. This can be a time consuming process, of adjusting and waitingfor the desired results.

The systems used previously have many undesirable features. First andforemost is the potential of the hydraulic cylinder to leak at any ofthe locations along its length where the ports are located. The electricover hydraulic switches are prone to failure, and their life span isvery limited due to the fact that they are a mechanical switch. Theoperator also has to uncouple and recouple these switches manually andput them into the positions required for the desired stroke length.There is also a danger of spilled hydraulic fluid any time this is done.

The preferred system does not require pressure ports through whichfluids could leak, and has explosion proof classification in class 1division 2 areas around the well head, which reduces the risk of wellhead explosions.

In addition, as the system is completely sealed, piston 14 may be moreeasily serviced. Referring to FIG. 5, piston 14 is lowered to the lowerend 30 of piston cylinder 12 and locked into place using a commonwellhead lock or safety valve, such as a blowout preventer 38. As shown,once locked down, the wellbore is sealed, such that cylinder 12 may beremoved to allow access to piston 14 without the use of a service rig tohold the weight of the rod string. At this point, piston 14 may beserviced or replaced while keeping the well shut-in and allows the fullweight of the string to be held independent of any lifting equipment,while maintaining full containment on the well. The piston design allowsthe cylinder to be removed without disconnecting the sucker rod, polishrod and exposing the wellhead to the atmosphere. This function allowscost savings and easy servicing.

Most of the hydraulic cylinders presently manufactured use a steel outertube with steel piston rod and steel piston. In magnetics, it is knownthat steel acts as a shunt, where the magnetic lines of flux will notpass through steel. The present system is manufactured usingnon-magnetic materials. For example, in one embodiment, the outercylinder tube was manufactured using non-magnetic stainless steel, andthe piston was manufactured using non-magnetic aluminum and the pistonrod was manufactured using high quality steel. The aluminum pistonhouses may be rare earth neomidium iron boron magnet with high strengthmagnetic characteristics.

The presently described system enables the operator to know the positionand the speed of the hydraulic cylinder within a fraction of an inch, ifdesired. The preferred embodiment uses and LDT sensor bar that spans thefull length of the non-magnetic stainless steel cylinder and enables theuser to adjust the hydraulics to speed up or slow down to the programmedstrokes per minute. The stroke length can be programmed to start andstop anywhere between various switch points along the length of thehydraulic cylinder to an accuracy of up to 0.1″in some embodiments.

Traditional electric over hydraulic switches used on most hydraulic pumpjacks utilize a diaphragm which, when hydraulic pressure pushes againstthis diaphragm it either opens or closes a mechanical toggle switch.Because of the mechanical nature of this design it is limited to thenumber of times it can be activated.

In this patent document, the word “comprising” is used in itsnon-limiting sense to mean that items following the word are included,but items not specifically mentioned are not excluded. A reference to anelement by the indefinite article “a” does not exclude the possibilitythat more than one of the element is present, unless the context clearlyrequires that there be one and only one of the elements.

The following claims are to be understood to include what isspecifically illustrated and described above, what is conceptuallyequivalent, and what can be obviously substituted. Those skilled in theart will appreciate that various adaptations and modifications of thedescribed embodiments can be configured without departing from the scopeof the claims. The illustrated embodiments have been set forth only asexamples and should not be taken as limiting the invention. It is to beunderstood that, within the scope of the following claims, the inventionmay be practiced other than as specifically illustrated and described.

1. A switching assembly for a hydraulic pump jack, comprising incombination: a non-magnetic cylinder with an exterior surface and aninterior surface that defines an interior bore; a piston reciprocallymovable within the interior bore of the cylinder, the piston havingcircumferential sealing means to engage the interior surface of thecylinder; a magnetic element carried by the piston; a fluid sourcesupplying a working fluid to the cylinder, wherein the piston is movedby injecting working fluid into the cylinder; at least one magneticsensor externally mounted adjacent to the non-magnetic cylinder thatsenses at least a top of a piston stroke and the bottom of the pistonstroke; a controller that receives signals from the magneticallyactuated sensor as the magnet element carried by the piston comes inproximity with and influences the at least one magnetic sensor, thecontroller controlling piston positioning by selectively controlling theworking fluid supplied by the fluid source to the cylinder.
 2. Theswitching assembly of claim 1, wherein the cylinder has a lower end andan upper end, the upper end being higher than the lower end, the workingfluid serving to raise the piston from the lower end toward the upperend, and gravity serving to return the piston from the upper end to thelower end.
 3. The switching assembly of claim 1, wherein the magneticsensor is a linear displacement transducer sensor bar that extends alongthe height of the non-magnetic cylinder.
 4. The switching assembly ofclaim 1, further comprising a seal for sealing the well when the pistonis in a lower position, the non-magnetic cylinder being removable toexpose the piston in the lower position.
 5. A switching assembly for ahydraulic pump jack, comprising in combination: a non-magnetic cylinderwith an exterior surface, an interior surface that defines an interiorbore, a lower end and an upper end that is higher than the lower end; apiston reciprocally movable within the interior bore of the cylinder,the piston having circumferential sealing means to engage the interiorsurface of the cylinder; a magnetic element carried by the piston; afluid source supplying a hydraulic working fluid to the cylinder,wherein the piston is raised from the lower end toward the upper end byan injection of working fluid into the cylinder; a linear displacementtransducer (LDT) sensor bar mounted to the exterior surface of thecylinder, the LDT sensor bar continuously measuring the position of thepiston; and a controller that receives signals from the LDT sensor baras the magnet element carried by the piston travels along thenon-magnetic cylinder, the controller controlling piston movement byselectively controlling the working fluid supplied by the fluid sourceto the cylinder in response to the received signals.
 6. The switchingassembly of claim 5, wherein the piston returns from the upper end tothe lower end by force of gravity.
 7. The switching assembly of claim 5,further comprising a seal for sealing the well when the piston is in alower position, the non-magnetic cylinder being removable to expose thepiston in the lower position.